A traveling wavetube with improved thermal and magnetic circuitry



Aug. 20, 1968 (5, w. WASHBURN 3,398,315

TRAVELING WAVE TUBE WITH IMPROVED THERMAL AND MAGNETIC CUITRY Filed Aug 1965 FlG.l.

OUTPUT RF INPUT VOLTAGE SOURCE INVENTOR. George W. Wushburn QQWQM Q ATTORNEY WITNESSES We KW X 2 United States Patent A TRAVELING WAVE TUBE WITH IMPROVED THERMAL AND MAGNETIC CIRCUITRY George W. Washburn, Horseheads, N.Y., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a

a corporation of Pennsylvania Filed Aug. 19, 1965, Ser. No. 480,893 7 Claims. (Cl. 315-35) This invention relates to electron beam systems and more particularly to those systems utilizing a magnetic focusing structure.

One particular application of this invention is in electronic tube devices of the traveling wave type. In a traveling wave tube an electron beam is projected along an extended path for interaction with an electromagnetic wave. The electromagnetic wave is provided on a slow wave propagating structure and may be in the form of a helix. It is Well known that the electron beam gives up energy to the slow wave structure resulting in amplificationof a microwave signal traveling on the slow wave structure.

It is necessary to provide focusing means for the electron beam to prevent excessive interception of the electron beam by the slow wave structure. One method of focusing the electron beam is a periodic permanent magnet system. In this type of configuration, a succession of hollow cylinders of a magnetic material such as a soft iron are disposed along and surround the electron beam path. A succession of small permanent magnets are bridged between successive magnetic cylinders forming a series of converging magnetic lenses which establish longitudinal magnetic fields of substantially asymmetry along portions of the electron path corresponding to the gaps formed between successive magnetic cylinders. The pole faces of the permanent magnets are oriented to introduce a reversal of the longitudinal magnetic field along portions of the electron path corresponding to successive gaps so that the magnetic field will fall off sharply with distance away from the magnetic path.

It is found, that even with the periodic type focusing system, some of the electron beam energy is delivered to the slow wave circuit in the form of heat due to the beam striking the slow wave structure. In high power, high efficiency tubes, this heat can be appreciable and the heat must flow radially outward to cooling type fins. It is thus obvious that a good thermal path must be provided from the slow wave structure to the exterior portion of the tube. At the same time, the periodic magnetic focusing arrangement determines the percentage of the electron beam striking the slow wave structure. In order to obtain the required magnetic fieldstrength with a minimum weight and size and keep within the capabilities of available and desired magnetic materials, it is desirable to extend the pole pieces or cylinders close to the electron beam. Good magnetic flux carrying materials, usually soft iron, are relatively poor heat conductors.

It is accordingly an object of this invention to provide an improved focusing arrangement for providing good thermal conduction of the heat away from the slow wave structure as well as providing good magnetic flux conduction into the region of the electron beam.

It is another object to provide an improved electron beam focusing system.

It is another object to provide an improved electron beam focusing system combined with good thermal conduction from the interior region.

It is still another object to provide an improved traveling wave tube in which the focusing system provides good thermal conduction and good flux conduction between the interior region adjacent the electron beam to the exterior region of the envelope.

3,398,315 Patented Aug. 20, 1968 ice Briefly, the present invention accomplishes the above cited objects by providing a pole piece assembly of good magnetic fiux conduction properties with addition means to provide a good thermal path for removing the heat from the interior region of the focusing system.

Further objects and advantages of the invention will become apparent as the following description proceeds and features of novelty which characterize the invention will be pointed out in particularity in the claims annexed to and forming a part of this specification.

For a better understanding of the invention, reference may be had to the accompanying drawings, in which:

FIGURE 1 is an axial sectional view of a traveling Wave tube embodying the invention;

FIG. 2 is an enlarged view of a portion of FIG. 1; and

FIG. 3 is a sectional view similar to FIG. 2 illustrating a modification of the invention in accordance with the teaching of the invention.

Referring to FIG. 1, a traveling wave tube 10 is illustrated. The traveling wave tube 10 is comprised of an elongated evacuated envelope 12 of a suitable non-magnetic material such as Monel, copper, or stainless steel. The envelope 12 is provided with an electron gun 14 at one end of the envelope and includes at least a cathode 16, a focusing electrode 18, and an anode 19 for forming and focusing an electron beam. A target or collector electrode 20 is positioned at the opposite end of the envelope 12 for collecting the electrons generated by the electron gun 14. The collector 20 is maintained at a suitable potential with respect to the cathode 16 by means of a suitable lead-in connection from a voltage source 22. The electrodes are shown diagrammatically in that the details are well known and any suitable structure may be utilized.

Interposed between the electron gun 14 and the collector 20 is a suitable slow wave interaction circuit illustrated as a helical coil conductor 24. The slow wave assembly 24 may also serve as an accelerating electrode for the electron beam and may be maintained at a suitable potential with respect to the cathode 16 of the electron gun 14. At each end of the slow wave structure 24, coupling structures are provided to external transmission lines by any suitable means. In the specific embodiment shown, the input signal is applied to the helix 24 by a lead-in 26. In the specific embodiment shown, an output coupling means 32 in the form of a lead-in is connected to the helix 24 and energy is transferred therefrom for utilization in an output circuit. It is obvious that a number of different types of devices may be utilized for coupling to the slow wave structure 24. The helix 24 is supported within the envelope 12 by means of spacer members 27 in thermal contact with the helix 24 and the envelope 12 and of suitable materials such as BeO or A1 0 Disposed along the path of the electron beam from the cathode 16 to the collector 20 is a periodic magnetic focusing system 40. In the specific embodiment shown, the periodic focusing system 40 consists of uniformly spaced annular pole pieces 46 of a suitable material having a high magnetic permeability such as soft iron or an iron base alloy. A series of ring-shaped magnets 48 are disposed across successive gaps between the pole pieces 46. The magnets 48 are magnetized axially and arranged coaxially so that the adjacent magnets exert oppositely directed magnetic fields. The magnets 48 may be of a suitable type such as ferrite permanent magnets. This provides along the path of the electron flow a succession of regions of longitudinal magnetic fields with the direction of the magnetic fields reversing within each successive region. Preferably, the pole pieces 46 have a substantially T-shaped cross-section as illustrated in FIGS. 2 and 3.

Referring in detail to FIGS. 2 and 3, the pole piece 46 consists of two halves 50 and 52 with a layer 54 of heat conductive material such as copper or a copper base alloy therebetween. The layer 54 is annular in shape and in one specific embodiment has a thickness of about .020 inch and an outer diameter of about 1.250 inches. In this manner, a path is provided by the ring 54 to conduct the heat outwardly from the envelope 12 while the two halves 50 and 52 carry the magnetic flux from the magnets 48 close to the electron beam region. Thus, the pole piece 46 satisfies both of the requirements of thermal conduction and magnetic conduction.

In FIG. 3, there is shown another embodiment of the invention in which a pole piece 56 is provided. The pole piece is a unitary structure with a copper plating of about .003" in thickness on the outside surface of the pole piece 56. The copper plating 58 may be provided by plating or other suitable means. The structure illustrated in FIG. 3 results in a reduced magnetic flux on the electron beam because of the air gap between the pole piece 56 and the magnet 48. In this respect the structure as shown in FIGS. 1 and 2 is superior.

By the technique illustrated in FIGS. 1 and 2 in separating the thermal and magnetic paths, each path can be optimized without interfering with each other. A tubular sheath 60 is provided about the focusing arrangement 40 and is in thermal and physical contact with the ring members54. The sheath or heat radiating member 60 may be of a suitable thermal conductive material such as copper and may be provided with fins 62 thereon of a similar material for air or liquid cooling the structure.

In the operation of the device illustrated in FIG. 1, the electron beam generated by the electron gun 14 is projected along the axis of the envelope 12. Upon interaction with the slow wave structure 24, the beam of electrons is spread due to the interaction with the circuit and space charge effects. The magnetic focusing arrangement 40 provides focusing for the electrons within the electron beam. Those electrons that are collected on the slow wave structure 24 generate heat. This heat is removed by conduction .through the spacers 27 to the envelope 12. The heat is then removed from the envelope 12 by means of the plurality of thermal conductive rings 54 to the outer heat conductive sheath 60 and fins 62. In this manner the heat generated within the helix 24 may be removed from the structure and provide a more efiicient and higher power capability traveling wave tube.

While there has been shown and described what are at present considered to be the preferred embodiments of the invention, modifications thereto will readily occur to those skilled in the art. It is not desired, therefore, that the invention be limited to the specific arrangements shown and described and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

I claim as my invention:

1. A traveling wave tube comprising an envelope, an electron gun positioned therein for generating and directing an electron beam along an extended beam path within said envelope, a series of pole pieces alternating with a series of axially polarized permanent magnets disposed about said envelope with like poles adjacent to each other, said pole pieces including a first portion of magnetic material for establishing with said magnets a periodic spatially alternating beam focusing magnetic field along said beam path, said pole pieces including a second portion of non-magnetic material of better thermal conducting properties than said magnetic material extending inwardly into thermal contact with said envelope and outwardly beyond said first portion of said pole pieces and a heat radiating means in thermal contact with said second portion of said pole pieces for establishing a heat conductive path from said envelope.

2. A traveling wave tube comprising an envelope, an electron gun positioned therein for generating and directing an electron beam along an extended beam path within said envelope, focusing means including annular magnets external of said envelope, annular magnetic conducting means provided intermediate said magnets and extending radially inwardly into proximity .of said envelope to provide magnetic effects in close proximity to said beam, an annular non-magnetic means of good heat conducting properties extending radially inwardly into proximity of'said envelope for conducting heat away from said envelope and to a heat radiationmeans surrounding said focusing means inv thermal .contact with said annular non-magnetic means of good heat conducting properties.

3. A traveling wave tube comprising an envelope, an electron gun positioned therein for generating and directing an electron beam along an extended beam path within said envelope-focusing means. including annular magnets external of said envelope, a pair of annular magnetic conducting means-provided intermediate of two of said magnets and. extending radially inwardly into proximity of said envelope to provide magnetic effects in close proximity to said beam, and an annular non-magnetic metallic means of good heat conducting properties extendingradially inwardly into proximity of said envelope and positioned between said pair of magnetic conducting means for conducting heat away from said envelope.

4. An electron device comprising an envelope, an electron gun positioned therein for generating and directing an electron beam along an extended beam path within said envelope, focusing means including at least two annular magnets external of said envelope, first and second annular magnetic conducting members provided intermediate said magnets and extending radially inwardly into proximity of said envelope to provide magnetic focusing effects in close proximity to said beam, and an annular non-magnetic metallic member of good heat conducting properties positioned between said first and second annular magnetic conducting members and extending radially inwardly into proximity of said envelope for conducting heat away from said'envelope.

5. A traveling wave tube comprising an envelope, an electron gun positioned therein for generating and directing an electron beam along an extended beam path within said envelope, a wave propagating member positioned within said envelope and along said extended beam path for interacting with said electron beam, said wave propagating member supported within said envelope and provided with thermal conductive means between said envelope and said wave propagating member, a focusing means including two annular magnets external of said envelope and forming a cylindrical outer surface, a pair of annular magnetic material members positioned intermediate said annular magnets and extending radially inwardly to provide magnetic focusing effects in close proximity to said beam path and annular non-magnetic metallic material members provided between each of said pair of annular magnetic'material members-and extending radially inwardly into'contact with said envelope and extending outwardly beyond said cylindrical outer surface.

6. A traveling wave tube comprising an envelope, an electron gun positioned therein for generating and directing an electron beam along an extended beam path within said envelope, a slow wave propagating member positioned within said envelope and along said extended beam path for interacting with said electron beam, said slow wave propagating member supported within said envelope and provided with thermal conductive means between said envelope and said wave propagating member, an electron beam focusing means including two annular magnets external of said envelope and forming a cylindrical outer-surface, a pair of annular magnetic members'positioned intermediate said annularmagnets and extending radially inwardly to provide magnetic focusing effects in close proximityto said beam path, a

non-magnetic-metallie member provided between said pair of magnetic members extending radially inwardly into contact with said envelope and extending outwardly beyond said cylindrical outer surface and heat radiating means disposed in thermal conducting contact with said non-magnetic metallic member.

7. A traveling wave tube comprising an envelope, an electron gun positioned therein for generating and directing an electron beam along an extended beam path within said envelope, a wave propagating member positioned within said envelope and along said extended beam path for interacting with said electron beam, said wave propagating member supported within said envelope and provided with thermal conductive means between said envelope and said 'wave propagating member, a focusing means including two magnets external of said envelope, a pair of magnetic conducting members positioned intermediate said magnets and extending radially inwardly to provide magnetic focusing effects in close proximity to said beam path, a non-magnetic metallic material member of better heat conducting property than said magnetic conducting members provided between said pair of magnetic members extending radially inwardly into contact with said envelope and extending outwardly into thermal conducting contact with a heat radiating member.

References Cited UNITED STATES PATENTS 2,741,718 4/1956 Wang 315-3.5 2,970,240 1/ 1961 Iversen 3153.5 2,971,113 2/1961 Nygard 3153.5

HERMAN KARL SAALBACH, Primary Examiner.

S. CHATMON, IR., Assistant Examiner. 

1. A TRAVELING WAVE TUBE COMPRISING AN ENVELOPE, AN ELECTRON GUN POSITIONED THEREIN FOR GNERATING AND DIRECTING AN ELECTRON BEAM LONG AN EXTENDED BEAM PATH WITHIN SAID ENVELOPE, A SERIES OF POLE PIECES ALTERNATING WITH A SERIES OF AXIALLY POLARIZED PERMANENT MAGNETS DISPOSED ABOUT SAID ENVELOPE WITH LIKE POLES ADJACENT TO EACH OTHER, SAID POLE PIECES INCLUDING A FIRST PORTION OF MAGNETIC MATERIAL FOR ESTABLISHING WITH SAID MAGNETS A PERIODIC SPATIALLY ALTERNATING BEAM FOCUSING MAGNETIC FIELD ALONG SAID BEAM PATH, SAID POLE PIECES INCLUDING A SECOND PORTION OF NON-MAGNETIC MATERIAL OF BETTER THERMAL CONDUCTING PROPERTIES THAN SAID MAGNETIC MATERIAL EXTENDING INWARDLY INTO THERMAL CONTACT WITH SAID ENVELOPE AND OUTWARDLY BEYOND SAID FIRST PORTION OF SAID POLE PIECES AND A HEAT RADIATING MEANS IN THERMAL CONTACT WITH SAID SECOND PORTION OF SAID POLE PIECES FOR ESTABLISHING A HEAT CONDUCTIVE PATH FROM SAID ENVELOPE. 